Conveyors consisting of a continuous or broken-blade helix or screw fastened to a shaft and rotatably driven so that the revolving screw advances material in a predetermined direction are well known. More recently, a portion of the helix or screw in such conveyors has been replaced by individual paddles. The paddles are useful for mixing the conveyed material and for moving the material in a desired direction which may be different than the direction of movement determined by the revolving screw section of the conveyor.
In particular, screw conveyors, or augers, have been advantageously used on paving machines to convey road building materials transversely across the roadbed prior to being leveled and at least partially compacted by a trailing screed assembly. For example, the BG-200B Series Asphalt Pavers manufactured by the assignee of the present invention have hydrostatically driven dual left and right side screw conveyors which operate independently of each other to distribute asphalt paving material across the roadbed, transverse to the direction of travel of the paving machine.
Aggregate mixes such as asphalt paving materials are subject to segregation during movement Transverse segregation of the material is a problem that frequently occurs during lateral distribution of the paving material onto a roadway surface. This problem, more commonly known as "center streak" occurs when a disproportionate amount of coarse aggregate is deposited at the center of the mat being formed. Typically, asphalt material is transferred from a surge bin, or hopper, to the roadway surface, including an area at the transverse center of the machine which lies under a centrally disposed chain drive case for the lateral distribution screw. If not properly mixed, or otherwise inhibited from segregation, coarse aggregate in the asphalt mix tends to roll under the central drive case, fill the underlying region, and inhibit the entrance of smaller aggregate and fines. This produces an area, or strip, of coarse aggregates with few fines to fill voids and bind the mix together. Without the necessary binding materials, the coarse aggregate breaks loose from the road surface, producing a condition commonly known as "ravelling."
In response to this problem, the screw conveyors may have individual paddles disposed near their inboard ends to mix and direct a portion of the paving material inwardly toward the transverse center of the paving machine. This solution works well for some paving materials, but less desirably for others. For example, if the orientation of the paddles is designed to provide the optimum pitch angle for mixing and conveying a selected hot asphalt mix, it will be less effective in distributing other mixes, such as a cold mix or an in-place recycled mix. As a result, it is often necessary to compromise the designed pitch angle of the paddles to provide generally acceptable, but not optimum, mixing and distribution of the more commonly used material mixtures.
The present invention is directed to overcoming the problems set forth above. It is desirable to have a screw conveyor that can be selectively adjusted for changes in the flow characteristics of the conveyed material. Furthermore, it is desirable to have a screw conveyor in which mixing and flow-directing paddles are selectively adjustable for use on a wide variety of materials having dissimilar flow characteristics.